"Вестник МГСУ"

Experimental study of bearing capacity of samples of two series performed by semiautomatic welding in CO2 on the axis, and by robotic welding machine in mixture (CO2 + Ar), is presented. Welds of constant cross section, welds with extended leg on end sections, and welds in the form of two dowels on end sections were performed. Efficiency of pilot samples of the first series (with extended leg on end sections by way of a smooth transition) defined by the ratio of weld metal volume to a crushing load reaches 28 % relative to samples with a leg constant as per length. Samples of the first series with an extended leg on end sections also showed efficiency increased to 17 %. According to the second series samples test results, the exceeding of bearing capacity of the samples performed with an extended leg on end sections by 24 % in comparison with the samples with a leg of constant cross section was determined. Samples of the second series performed in the form of two dowels on end sections demonstrated the exceeding of the relative bearing capacity by 42 % in comparison with the samples with a continuous leg of constant cross-section.

The article represents a brief overview of the properties of steel type 14X2GMR (Russian standards), a high-performance synergetic structural steel exposed to different modes of heat treatment.
The author demonstrates that the best set of the steel properties was obtained upon its normalization (Option 5). An alternative option is Option 1 (water quenching). This steel demonstrates its ≈ 1,0, which indicates the proximity between the uniform δр value and the concentrated δc value as the constituents of δ, the elongation value.
The best set of δр ,Ψр ,p, c, Кзт and p/c values is demonstrated by the steel at the normal temperature of 20 °C. An alternative set of criteria properties is identified at -60 °С.
The final choice of the optimal heat treatment mode and the operating temperature is recommended to be based on the maximal values of = p/c and the static viscosity
c = 0,5(k - σT)1n[1/(1 - Ψ)].
Given the resistance of steel to cracking during welding (Δ= 1,5; PSK= -0,25<0), it can be recommended for heavy-duty welded parts and assemblies.

Diagnostics of residual welding stresses based on the layout of temperature traces that (i)
characterize isothermals of maximal temperatures within a thermal cycle of welding and (ii) are
retained on the metal surface of a welded joint represents a prospective trend of non-destructive
methods of control of residual stresses. The traces to be examined include both natural (temper colours
and fusion boundaries) and artificial traces formed on the metal surface in the course of fusion
of pre-applied temperature indication lines (lines of temperature indication markers, etc.).
The layout of temperature traces assures the uniqueness of the solution to an inverse problem
of a thermal cycle of welding reconstructed by the researcher. The kinetic pattern of alterations of
the stress-deformation state (SDS) of a welded joint in the course of welding, as well as the pattern
of residual stresses (the latter solely require the information concerning the cooling stage of a thermal
cycle) can be identified on the basis of the reconstructed thermal cycle model.
In the paper, the procedure of reconstruction of a thermal cycle on the basis of temperature
traces is exemplified by resistance flash-butt welds of metal rods. Despite the one-dimensionality of
the model, it presents a widespread type of welding of rails and accessories of building structures;
this type of welding is used to connect edges of steel pipes, including those that have a big diameter
and are used as underwater gas pipelines. Residual welding stresses of joint welds and the adjacent
area can be identified with the help of a thermal marker.